This invention relates to a method and apparatus for electrochemically producing high porosity, high activity copper powders for high-temperature thermochemical water splitting.
Copper is substantially non-reactive with HCl at room temperature for producing hydrogen. However, at elevated temperatures, e.g. 425° C., copper reacts with HCl to form hydrogen and copper (1) chloride (CuCl). To produce copper and HCl, the copper (1) chloride needs to be cycled. Thus, the net reaction of the entire process is2H2O→2H2+O2 
The key component of the Cu—Cl cycles is the electrochemical cycle, which has numerous potential barriers that must be overcome. First, there is the issue of materials. The product of CuCl after the electrochemical cycle is copper (2) chloride (CuCl2), which is a strong oxidant and which is highly corrosive. Metallic materials, such as stainless steels, are not suitable for use as a reservoir, electrode plate, or cycle tube line. Second, there is the issue of recycle and separation requirements. The efficiency of the recycle is related to the ion transport rate of the separation membrane, an anion exchange membrane, in the electrochemical cell. Enhancement of the cell efficiency requires that the ionic conductivity be high. In addition, the membrane must be strong and have substantial longevity. Also, because the solubility of CuCl in water is very low, on the order of 0.0062 g/100 ml water, the amount of CuCl in the solution must be increased. Third, there is the issue of electrochemical design. In particular, the electrochemical cell must have high weight/volume power density and high efficiency; and the cell must distribute electricity uniformly in the reaction region. Finally, there is the issue of a skin effect. That is, CuCl2 reacts with water at 325° C., producing as a product Cu2OCl2, which, due to the coverage of the electrodes by Cu2OCl2, retards the reaction between water vapor and CuCl2.